To make a long story short: Conventions are not your playground. You do not get to ignore people's personal boundaries just because you are wearing a costume. If you or your fandom in general do harass people, expect con-goers to avoid your fandom. Don't be surprised if people talk about your bad behavior. Instead, acknowledge what's wrong with your fandom's behavior and understand why people are suspicious; do your best to change the community. Or maybe, if you don't like what this community does, consider that maybe it's not a community that you should be a part of, much less defending?
There are rules at conventions. You are expected to read the rules of the con. In the same way you'd have to pay if you lost your con badge to get a second one or return to your hotel to change clothes if your costume contains contraband, if you harass someone you will have to pay the consequences. If the person harmed goes to con staff, you could have your pass taken away or even be banned from the con.
More than that, if you and many members of your fandom treat the con as a personal playground and take that as an opportunity to harass, catcall, or otherwise abuse other con-goers, guess what? You don't get to be upset that your fandom has a bad name at cons.